Zoom lens and imaging apparatus

Abstract

A zoom lens includes a positive first lens group, a negative second lens group, a positive third lens group, and a fourth lens group. The first through third lens groups move such that the distance between the first and second lens groups is greater while the distance between the second lens group and the third lens group is less at the telephoto end compared to the wide angle end, and the fourth lens moves with the third lens group. The third lens group includes a fixed positive subgroup, including at least one positive lens and one negative lens, and a movable subgroup provided toward an image side of the fixed lens group including one negative lens that moves perpendicular to an optical axis to correct an image plane when camera shake occurs. The fourth lens group includes a fixed subgroup and a movable subgroup that moves during focusing operations.

What is claimed is: 
     
       1. A zoom lens, comprising:
 a first lens group having a positive refractive power; 
 a second lens group having a negative refractive power; 
 a third lens group having a positive refractive power; and 
 a fourth lens group having a positive or a negative refractive power; provided in this order from an object side; 
 the first lens group, the second lens group, and the third lens group moving such that the distance between the first lens group and the second lens group is greater while the distance between the second lens group and the third lens group is less at the telephoto end compared to the wide angle end, and the fourth lens moving integrally with the third lens group; 
 the third lens group substantially consisting of a fixed third lens group having a positive refractive power as a whole, constituted by at least one lens having a positive refractive power and at least one lens having a negative refractive power, and a movable third lens group provided more toward an image side than the fixed third lens group constituted by a single lens having a negative refractive power that moves in a direction perpendicular to an optical axis to correct an image plane when camera shake occurs; and 
 the fourth lens group substantially consisting of a movable fourth lens group that moves along the optical axis during focusing operations and a fixed fourth lens group which is fixed with respect to the direction of the optical axis during focusing operations. 
 
     
     
       2. A zoom lens, comprising:
 a first lens group having a positive refractive power; 
 a second lens group having a negative refractive power; 
 a third lens group having a positive refractive power; and 
 a fourth lens group having a positive or a negative refractive power; provided in this order from an object side; 
 the first lens group, the second lens group, and the third lens group moving such that the distance between the first lens group and the second lens group is greater while the distance between the second lens group and the third lens group is less at the telephoto end compared to the wide angle end, and the fourth lens moving along a trajectory different from that of the third lens group; 
 the third lens group substantially consisting of a fixed third lens group having a positive refractive power as a whole, constituted by at least one lens having a positive refractive power and at least one lens having a negative refractive power, and a movable third lens group provided more toward an image side than the fixed third lens group constituted by a single lens having a negative refractive power that moves in a direction perpendicular to an optical axis to correct an image plane when camera shake occurs; and 
 the fourth lens group substantially consisting of a movable fourth lens group that moves along the optical axis during focusing operations and a fixed fourth lens group which is fixed with respect to the direction of the optical axis during focusing operations. 
 
     
     
       3. A zoom lens as defined in  claim 1 , wherein:
 the movable fourth lens group and the fixed fourth lens group have refractive powers of mutually different signs. 
 
     
     
       4. A zoom lens as defined in  claim 1 , wherein:
 the fixed third lens group comprises at least two lenses having positive refractive powers. 
 
     
     
       5. A zoom lens as defined in  claim 1  that satisfies Conditional Formula (1) below:
   0.8 <|f 3 IS/f 3|<2.6  (1)
 
 wherein f3IS is the focal length of the movable third lens group, and f3 is the focal length of the third lens group. 
 
     
     
       6. A zoom lens as defined in  claim 5  that satisfies Conditional Formula (1-2) below:
   0.9 <|f 3 IS/f 3|<2.4  (1-2).
 
 
     
     
       7. A zoom lens as defined in  claim 5  that satisfies Conditional Formula (1-3) below:
   1.0 <|f 3 IS/f 3|<2.3  (1-3).
 
 
     
     
       8. A zoom lens as defined in  claim 1  that satisfies Conditional Formulae (2) and (3) below:
   1.2 <|f 3 IS/fw|< 3.5  (2)
 
   0.3 <|f 3 IS/ft| <1.3  (3)
 
 wherein f3IS is the focal length of the movable third lens group, fw is the focal length of the entire system at the wide angle end, and ft is the focal length of the entire system at the telephoto end. 
 
     
     
       9. A zoom lens as defined in  claim 8  that satisfies Conditional Formula (2-2) below:
   1.3 <|f 3 IS/fw|< 3.4  (2-2).
 
 
     
     
       10. A zoom lens as defined in  claim 8  that satisfies Conditional Formula (2-3) below:
   1.4 <|f 3 IS/fw|< 3.3  (2-3).
 
 
     
     
       11. A zoom lens as defined in  claim 8  that satisfies Conditional Formula (3-2) below:
   0.4 <|f 3 IS/ft| <1.1  (3-2).
 
 
     
     
       12. A zoom lens as defined in  claim 1 , wherein:
 the first lens group substantially consists of two lenses, which are a lens having a negative refractive power, and a lens having a positive refractive power, provided in this order from the object side. 
 
     
     
       13. A zoom lens as defined in  claim 1 , wherein:
 the fourth lens group has a positive refractive power; and 
 the movable fourth lens group has a positive refractive power. 
 
     
     
       14. A zoom lens as defined in  claim 1  that satisfies Conditional Formula (4) below:
   0.05 <|f 4 F/f 4|<1.00  (4)
 
 wherein f4F is the focal length of the movable fourth lens group and f4 is the focal length of the fourth lens group. 
 
     
     
       15. A zoom lens as defined in  claim 1 , wherein:
 the second lens group substantially consists of three lenses, which are a lens having a negative refractive power, a lens having a negative refractive power, and a lens having a positive refractive power, provided in this order from the object side. 
 
     
     
       16. A zoom lens as defined in  claim 1 , wherein:
 only a fifth lens group, which is constituted by a single lens having a positive refractive power and which is fixed in the direction of the optical axis while changing magnification and during focusing operations, is provided as a lens group arranged more toward the image side than the fourth lens group. 
 
     
     
       17. A zoom lens as defined in  claim 1 , wherein:
 the movable fourth lens group substantially consists of a single lens. 
 
     
     
       18. A zoom lens as defined in  claim 1 , wherein:
 the fixed third lens group substantially consists of a lens having a positive refractive power, a lens having a negative refractive power, and a lens having a positive refractive power, provided in this order from the object side. 
 
     
     
       19. An imaging apparatus equipped with a zoom lens as defined in  claim 1 . 
     
     
       20. An imaging apparatus equipped with a zoom lens as defined in  claim 2 .